cheching date consisting from 3 drop boxes Using CompareValidator - asp.net

Question

I have 3 drop boxes which correspond to the Day, Month and A Year. After a user chooses a date I concatenate 3 strings and pass it to database.
My problem is how can I validate the date interactively before I pass it to database. To filter out invalid days like June 31 or Feb 30 which do not exist?
I thought about Comparevalidator. what I will do is I create 2 hidden textboxes, populate one with original user input string, and another one with user input string converted to date(if the date is not valid system should convert it to the nearest possible I think).
Than I compare those textBoxes using CompareValidator if they do not match error will be prompt. However somehow it doesn't work. Does anybody have an I idea why. or maybe someone knows less elaborate technique to check the date which is coming from drop boxes?
Will be grateful for any advice or suggestion.
Front end code:
<asp:DropDownList ID="Dates" runat="server" >
<asp:ListItem></asp:ListItem>
<asp:ListItem>01</asp:ListItem>
<asp:ListItem>02</asp:ListItem>
<asp:ListItem>03</asp:ListItem>
.......
<asp:ListItem>29</asp:ListItem>
<asp:ListItem>30</asp:ListItem>
<asp:ListItem>31</asp:ListItem>
</asp:DropDownList>
<asp:DropDownList ID="Monthes" runat="server" >
<asp:ListItem></asp:ListItem>
<asp:ListItem>January</asp:ListItem>
.......
<asp:ListItem>December</asp:ListItem>
</asp:DropDownList>
<asp:DropDownList ID="years" runat="server">
<asp:ListItem></asp:ListItem>
</asp:DropDownList>
<asp:TextBox ID="UserInput" runat="server"></asp:TextBox>
<asp:TextBox ID="ConvertedInput" runat="server"></asp:TextBox>
<asp:CompareValidator ID="CompareValidator1" class="errorMess" runat="server"
ControlToCompare="UserInput" ControlToValidate="ConvertedInput"
ErrorMessage="Invalid Date"></asp:CompareValidator>
Back end code:
If Not Page.IsPostBack Then
For count As Integer = 0 To 60
years.Items.Add(CurYear - count)
Next
End If
ConvertedInput.Visible = False
UserInput.Visible = False
.....
Bday = years.Text & "-" & Monthes.Text & "-" & Dates.Text
Dim TempDate As Date = CDate(Bday)
Dim ConvDate As String = TempDate.ToString("yyyy-MM-dd")
UserInput.Text = Bday
ConvertedInput.Text = ConvDate

Answer 1

you could use a customvalidator, build the date and verify it's a valid date. However I would recommend going with a straight textbox and using a UI library like jquery-ui to convert the textbox into a datepicker. you can then pull use DateTime.TryParse() to pull the date out of the textbox in the code behind.
the biggest advantage is only needing to deal with a single input and no string concatination/formatting.